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Roller Mills: What They Are and Why They're Great

Updated: Apr 29

Today's roller mills are an essential part of the American food production chain. Modern flour production depends on the use of grain roller mills to reduce wheat berries into flour. In addition, roller mills are vital to the processing of other grains, including the most important grain in the US today: corn.


Understanding why roller mills have taken over the grain production industry requires an understanding of both the benefits of roller mills and the historical forces that worked together to give them an edge in the market.


Millstones: The Last Great Thing

Before roller mills, grain processing was done by millstones. Millstones were themselves a tremendous innovation and offered huge benefits when they were invented in the last millennium BCE.

Handheld grain grinder that pre-dates the millstone, similar to the metate.
Handheld grain grinder prior to the millstone.

Before the invention of millstones, grain was ground using a variation on the metate: a handheld stone that was rubbed back and forth over an anvil stone. Not only was this method arduous, it resulted in the introduction of numerous rocks into the ground grain. This made the flour and any bread produced from it likely to damage a person's teeth. This is part of the reason why Egyptians needed so many dentists.


However, the Indians, Greeks, and Romans independently developed different forms of millstones. The millstone concept is similar to the metate: you have one stone that moves (often called the runner) while another remains stationary (called the sleeper or bedstone). Grain gets caught between the two stones and is ground down. At first, Olynthian runner millstones were moved by a lever over the bedstone. Later, Morgantina millstones were built in a rotary pattern. In Pompeii, relatively large mills were turned by levers pushed by slaves.


Millstone technology reached its peak when people began using wind or water power. This drove the mill better than human slaves or domestic animals could. At the same time, millstones were carved with intricate patterns of raised portions (called lands) and deep furrows, which progressed into finer channels called cracking. The pattern is divided into regular sections called harps or quarters.


Traditional windmill for grinding grain and flour in the Netherlands
Traditional grain windmill in the Netherlands

Millstones could produce more flour and when the right stone was used, there was much less grit. Millstones were ideal for grinding the soft type of wheat grown in Britain and the Low Countries. Because they were so successful, millstones were used for nearly two millennia with few changes other than the motive power.




The Invention of Roller Mills

However, millstones were not as good at grinding hard wheat, AKA spring wheat, which was mostly grown in Eastern Europe and the US. This hard grain had a bran that tended to shatter in the mill, making it harder to separate from the ground flour. Retained bran tended to make the flour spoil. Not only that, but flour with too much bran had an unappealing appearance and taste. If flour made with spring wheat was to be shippable, storable, and palatable, a new method of milling was needed.


The origins of the modern roller mill begin in Europe. Swiss engineer Jacob Sulzberger began experimenting with roller mills in the 1830s. His most successful installation was at Walzmühle, Budapest in Hungary. At this time, rollers were seen as a supplement to millstones. Stones were used for primary breaking of the grain, and the partly milled grain, called middlings or farina, then passed through rollers to be turned into flour. At Walzmühle, chilled cast-iron rolls were created in the local foundry for use in the roller mills. These rolls soon became the industry standard and were exported around the world through the 19th century. Some roller mills also used porcelain rollers, especially for processing semolina after stone grinding. By the 1870s, corrugated iron rolls began to replace the stones at the early stages of the grinding process.


Industrialization Gives Roller Mills the Edge

As roller mills started to pop up, the ancient class of millers, who had long been prominent figures in local communities, began to see a threat to their status and livelihood. They tried to improve the effectiveness of millstones by modifying the patterns on them, but by this time the technology had largely reached its pinnacle, and they couldn't gain much productivity. However, they retained some advantage: running roller mills from water or wind sources required extensive gearing, which made them complex, noisy, and prone to failure.


With the spread of steam power and belt drives, it became easier to power roller mills. The mills themselves were also quieter, more efficient, and more reliable. The development of more advanced steel made rollers more effective and more durable. By the end of the 19th century, mills were being refitted with rollers and the millstones discarded.


The Breadbasket of Democracy

One of the major centers of milling that changed over to roller mills was Minneapolis, the flour capital of the US. As the population of the US grew through the 19th century, demand for flour skyrocketed, and mills needed to keep up. In the 1860s, mills produced around 500 barrels of flour a day, but as the mills were changed into the much more efficient roller mills, productivity expanded dramatically. By the turn of the century, most mills produced 3000 barrels a day or more!


This was due in part to the use of a series of rollers that created a gradual reduction of wheat berries into flour. Not only was the process more efficient, it produced a higher quality flour that could sell for much higher prices. This drove the expansion of mills to improve profitability.

WW1 "Dont Waste Bread" poster showing the high demand for grain products.
Wheat production was in high demand during WW1

The improvements were timely. They let US wheat production compete on the world stage. Soon, exports of US wheat made the country an essential trading partner around the world. The wheat was especially in demand during the World Wars when grain production in Europe was dramatically disrupted. It was around this time that Automatic Equipment Manufacturing entered the picture. By WWII, our mills were helping grind the flour that fed the soldiers who won the war.


Rolled wheat had been plagued by one disadvantage: it was less nutritious than stone-ground wheat. This is because the processes of rolling grain led to a better separation of the nutritious bran and germ from the wheat, processing the less nutritious endosperm into flour. This eliminates most of the iron, vitamin A, and vitamin B1 from flour. However, fortification of the flour made the rolled flour comparable to ground flour.


Roller Mills and the Rise of King Corn

But roller mills can process all types and sizes of grain, and the growth of roller mills is intertwined with the most important crop in the US today: corn (maize).


Corn is a grain native to the Americas, but it remained a relatively under-cultivated crop for centuries. In part, this was because it was an inefficient crop to grow. Corn yields per acre remained stagnant until the 1930s when productivity per acre began to increase dramatically. This was due to two innovations: the hybridization of corn to make larger ears, and the development of industrial fertilizers that could satisfy corn's tremendous demand for nitrogen. Once corn productivity per acre began to soar, corn became more and more important as an animal feed.


Just in time, too, because by the time Americans returned from WWII and enjoyed the prosperity associated with their newly-won superpower status, they demanded more meat in their daily diet. As a result, corn demand also grew. From 1925 to 1945, corn production grew about 8%. From 1945 to 1965, corn production soared by 59%!


The spread of corn as animal feed was also facilitated by the development of highly efficient roller mills for cracking. These mills let farmers produce their own feed for a wide variety of animals, from chickens to cows.

High-capacity grain roller mill using PTO power.
Automatic high-capacity roller mill using PTO power.

Roller mills became standard equipment at most farms. They were produced in small sizes for use by small family farms and in high-capacity models that helped farmers develop larger-scale operations so America could enjoy the plentiful supply of meat that made it the model of a prosperous democracy, leading to victory in the Cold War. The widespread use of electricity and the development of PTO systems with tractors helped make roller mills even more flexible and useful.


Today, corn is the most important agricultural product in the US. American farmers grow about 8 times more corn than wheat.


The History of Roller Mills Continues

An early Automatic roller mill, taken nearly 100 years ago.
An early Automatic Roller Mill, nearly 100 years ago.

Today, Automatic Equipment Manufacturing continues to produce innovative roller mills. We draw on the extensive history of roller mills, including our own history that approaches a century of experience to make mills that incorporate the lessons of history to be efficient and durable. But we are also innovative, constantly seeking to make our mills produce better products, while becoming more efficient and easier to operate.


If you are looking for a roller mill to improve your farming or feedlot operation, we can help. Please contact Automatic Equipment Manufacturing today.

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